1. Technical Field
The present invention relates to a liquid discharge apparatus and a head unit.
2. Related Art
As an ink jet printer that discharges an ink and prints an image or a document, a printer that uses piezoelectric elements (for example, piezo elements) is known. The piezoelectric elements are provided respectively corresponding to a plurality of nozzles in a head unit and are respectively driven in response to drive signals and thereby, a predetermined amount of an ink (liquid) is discharged from the nozzle at a predetermined timing such that a dot is formed. The piezoelectric element is a capacitive load like a capacitor in terms of electric power. Therefore, a sufficient current supply is required to operate the piezoelectric elements of the nozzles.
Therefore, a configuration is employed, in which a drive signal amplified by using an amplifier circuit is supplied to a head unit such that the piezoelectric element is driven. Examples of the amplifier circuit include an amplifier circuit having a system of performing current amplification of a source signal before amplification through class AB amplification or the like. However, since the system is poor in energy efficiency, class D amplification has been proposed recently (see JPA-2010-114711).
In order to stabilize a frequency of self-oscillation in such class D amplification, a technique in which a phase locked loop (PLL) is provided in a feedback path for the self-oscillation such that a frequency of a signal of the self-oscillation is caused to approximate to a frequency of a reference signal has been proposed (see JP-A-2013-118628).
Incidentally, in the configuration in which the PLL is provided in the feedback path (loop) of the self-oscillation, an oscillation circuit for generating the reference signal is separately required, which results in complication of the circuit.
In addition, in this configuration, it has been pointed out that reproducibility of an output signal obtained by amplifying the source signal will not be good. One reason thereof is that not an output signal (final output) demodulated by a low-pass filter but a modulated signal in the middle of process is returned. The poor reproducibility of the output signal with respect to the source signal results in discharge failure of the ink and poor print quality.